PURPOSE: To obtain a wholly aromatic thermotropic copolyester having high heat resistance, a high melting point and the capability of forming a liquid crystal phase over the range from the melting point to the initial heat decomposition temperature by selecting a copolyester comprising terephthaloyl repeating units, 4-oxybenzoyl repreating units, dioxyarylene repeating units and 1,6- dioxynaphthalene repeating units.

CONSTITUTION: 0-50mol%, desirably 10-50mol terephthaloyl repeating units represented by formula I, 0-80 mol%, desirably 0-50 mol% 4-oxybenzoyl repeating units represented by formula II, 0-50 mol% dioxyarylene repeating units represented by formula III and 10-25 mol% 1,6-dioxynaphthalene repeating units (wherein Ar is a divalent aromatic residue; and A and B, which are the same or different from each other, are each -O- or -CO-) are randomly arranged to form a wholly aromatic thermotropic copolyester. This copolyester has a heat resistance of 350°C or above and a melting point of about 200 to 350°C and shows a liquid crystal polymer solution phase over the range from the melting point to the initial heat decomposition temperature.